Plasma and Fusion Research

Volume 13, 3402068 (2018)

Regular Articles

Neutron Flux Measurement Using a Fast-Neutron Scintillation Detector with High Temporal Resolution on the Large Helical Device
Kunihiro OGAWA1,2), Mitsutaka ISOBE1,2), Hiroki KAWASE2), Takeo NISHITANI1) and LHD Experiment Group1)
1)
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
2)
SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan
(Received 11 December 2017 / Accepted 2 May 2018 / Published 12 June 2018)

Abstract

To obtain rapid change of the neutron emission rate caused by magnetohydrodynamic (MHD) instabilities, measurements of the neutron flux with the high temporal resolution are made on the Large Helical Device (LHD) with a fast-neutron scintillation detector called neutron fluctuation (NF) operated in current modes. The time response of this detector is up to 5 microseconds. We checked the unwanted signal level caused by neutrons/gamma-rays inside the PMT. The intensity of the unwanted signal was negligibly small compared with the intensity of the scintillation signal as expected. The signal of NF has linear dependence with total neutron emission rate measured by neutron flux monitor in MHD quiet discharges. Rapid decreases of the neutron flux associated with bursting MHD modes excited in a neutral-beam-heated LHD plasma are observed with NF. We found that the neutron flux rapidly decreases within 2 ms.

Keywords

neutron flux measurement, fast neutron detector, the Large Helical Device, deuterium discharge

DOI: 10.1585/pfr.13.3402068

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